Synthetic linear hexamethylene adipamide polyamide yarns (often referred to as nylon 66) recently celebrated their 50th anniversary. An important use of such yarns is as textured multifilament yarns, e.g. for making apparel, such as hosiery. For many purposes, it is the high bulk that is desired in the textured yarns. For some years now, these bulky textured yarns have been prepared commercially in 2 stages; in a first process, nylon polymer has been melt spun into filaments that have been wound up into a (yarn) package at high speeds (of the order of 3000 meters per minute (mpm), so-called high speed spinning) as partially oriented yarn (sometimes referred to as POY) which is a feed yarn (or intermediate) for draw-texturing (and so sometimes referred to as DTFY for draw-texturing feed yarn); then, in a separate process, the feed yarns have been draw-textured on commercial texturing machines. These processes have been described in several publications, e.g. by Adams, in U.S. Pat. No. 3,994,121, issued 1976. Draw-texturing of various types of POY has been practiced commercially for more than 10 years on a very large scale. This has encouraged improvement of texturing machines. Accordingly, texturing machines have for some time had speed capabilities of well over 1000 mpm. But it has proved too difficult to obtain the desired bulky nylon 66 yarns at such high speeds, mainly because of limitations in the nylon POY that has been commercially available. So, in the U.S.A., for preparing the bulky nylon yarns that have been desired, nylon POY has for some years been textured commercially at speeds well below even 1000 mpm, i.e., well below the capability of the texturing machines, which could have been operated at significantly higher speeds.
Recently, Chamberlin et al in U.S. Pat. Nos. 4,583,357, and 4,646,514 have discussed such yarns, and their production via partially-oriented nylon (referred to by Chamberlin as PON). The disclosures of these "Chamberlin" Patents are incorporated herein by reference as background to aspects of the present invention.
Chamberlin discloses an improved (PON) spinning process and product by increasing the molecular weight of the nylon polymer well above the levels previously customary for apparel end uses. The molecular weight of nylon yarn was measured by relative viscosity (RV) determined by ASTM D789-81, using 90% formic acid. The apparel yarns were of nylon 66 of denier between 15 and 250; this denier range for apparel yarns is in contrast to that used for nylon carpet yarns, that have been made and processed differently, and are of different (higher) deniers, and some such carpet yarns had previously been of higher RV than for nylon apparel; Chamberlin mentions the expense and some difficulties of using higher RVs than conventional when making apparel yarns. Chamberlin's higher RVs were greater than 46, preferably greater than 53, and especially greater than 60, and up to 80 (for nylon 66). Chamberlin compared the advantages of such yarns over yarns having a nominal polymer RV of 38-40. Chamberlin discloses preparing PON by spinning at high speeds greater than 2200 mpm, and as high as 5000 mpm. Chamberlin describes how his high RV high-speed spun PON feed yarns were draw-textured at 750 or 800 mpm on a Barmag FK6-L900 texturing machine using a 21/2 meter primary heater at 225.degree. C. and a Barmag disc-aggregate with Kyocera ceramic discs, at a D/Y ratio of about 1.95. (As indicated by its name, the Barmag FK6-L900 texturing machine is itself capable of operation at 900 meters/minute, i.e. at speeds higher than disclosed by Chamberlin; texturing machines that are capable of operating at even higher speeds have been available commercially for several years). Chamberlin obtained crimp development values that were better than for 40 RV conventional yarn without excessive broken filaments (frays), or yarn breaks under these conditions.
Chamberlin explained the operable texturing tension range, within which the draw ratio may be changed (at a given draw roll speed) by adjusting the feed roll speed and so the draw-texturing stress or tension, which should be high enough for stability in the false-twist zone (to avoid "surging") and yet low enough to avoid (excessive) filament breakage. So adjustments were made to get maximum crimp development by operating with "maximum texturing tension" within this operable tension range. So, even if a feed yarn can be textured satisfactorily at a given speed and under other specified conditions, the operable texturing tension range may be quite narrow. A narrow texturing range (or "window") is commercially disadvantageous, as it limits the texturer.
This may be further understood by reference to FIG. 1, in which schematically texturing tensions are plotted against texturing speed. When one operates at a texturing speed V.sub.L, the average tension prior to twist-insertion (referred to as pre-disc tension T.sub.1) is shown by the large dot, but the actual along-end tension T.sub.1 is more accurately represented by a distribution of tensions; i.e., T.sub.1 .+-.-.DELTA.T.sub.1, where .DELTA.T.sub.1 represents approximately 3 times the standard deviation of the tension. Therefore, a stable texturing process requires that the minimum tension (T.sub.1 -.DELTA.T.sub.1), rather than the average pre-disc tension (T.sub.1), be sufficiently high to prevent surging. To increase the texturing speed from V.sub.L to V.sub.H, for example, by just increasing texturing speed (denoted as path A), would result in a condition wherein, although the average texturing tension might seem acceptable, the process would be unstable whenever T.sub.1 drops, so surging would occur. So, in practice, an increase in texturing speed is achieved by increasing the average T.sub.1 (see path B) by increasing the texturing draw ratio. Although such a higher draw ratio may avoid surging and so provide for a stable texturing process, the texturer may now obtain lower bulk, and may even experience broken filaments because of the increase in texturing tensions across the twist device. The post-disc tensions (T.sub.2) are usually greater than the pre-disc tensions (T.sub.1); in FIG. 1 this higher value is denoted by 2'. To increase bulk and eliminate broken filaments, the texturer must decrease T.sub.2 tensions from 2' to a lower point denoted by 2. This is usually achieved by increasing the relative disc-to-yarn speed ratio (D/Y) which slightly increases the pre-disc tensions (T.sub.1), but significantly decreases the post-disc tensions (T.sub.2) and, therefore, the T.sub.2 /T.sub.1 ratio. A concern with higher D/Y-ratios is increased disc wear and abrasion of the yarn. Another option is to increase texturing temperature, as the post-disc tension (T.sub.2) usually decreases more than the pre-disc tension (T.sub.1) as the temperature increases. This option, also, may be undesirable, as it will reduce the tensile strength of the "hot" yarn during twist insertion and increase the propensity for broken filaments.
This balancing of texturing draw ratio, the disc/yarn speed ratio, and the heater plate temperature is frequently referred to as the "texturing window" which narrows for a given texturing machine configuration with increasing texturing speed, as shown in FIG. 1; there are upper tension limits beyond which broken filaments occur, and even process breaks, and lower tension limits, below which surging occurs and poor along-end textured yarn uniformity.
SUMMARY OF THE INVENTION
According to the present invention, it has been found that incorporating a minor amount of a bifunctional polyamide comonomer with the regular nylon 66 diacid and diamide monomers provides the capability to improve further the texturing performance of the high RV nylon 66 multifilament draw-texturing feed yarns referred to above. Preferred bifunctional comonomers are .epsilon.-caprolactam and the monomer unit formed from 2-methyl-pentamethylene diamine and adipic acid, the latter being especially preferred as will be described hereinafter. .epsilon.-caprolactam is the monomer for preparing nylon 6 homopolymer, described by Chamberlin as inferior to nylon 66 for his purposes. It is believed that the monomer unit formed from 2-methyl-pentamethylene diamine and adipic acid has not been used for fibers. The behavior of the fibers of the present invention, however, give unexpected advantages over nylon 66 homopolymer fibers, as will be discussed herein. For convenience, sometimes herein, the use of the .epsilon.-caprolactam additive may be referred to as incorporating nylon 6, although it will be understood that a small amount of e-aminocaproic monomeric units from the .epsilon.-caprolactam, will be randomly distributed along the nylon 66 polymer chain (containing monomer units from the 6 diacid and from the 6 diamine monomers). Other monomer units will be also be randomly distributed. Also, for convenience, in comparing the performance of the fibers, especially in the Examples and Figures, the fibers of the invention incorporating .epsilon.-aminocaproic monomeric units may be referred to as N6,66, to distinguish from the homopolymer, referred to as N66. Similarly, fibers of the invention incorporating the monomer unit from 2-methyl-pentamethylene diamine (MPMD) and adipic acid may be referred to as Me5-6,66 and the monomer unit formed from the diamine and adipic acid (2-methyl-pentamethylene adipamide) may be referred to as Me5-6. Although this invention is not intended to be limited by any theory, we speculate that the minor amount of the monomer additive such as nylon 6 or Me5-6 provides this improvement because it is slightly different from the nylon 66 monomers, but is similar to the extent of being capable of hydrogen bonding; so it is believed that an improvement over homopolymer N66 may be obtained by using a minor amount of other comonomers similarly capable of hydrogen bonding, i.e. bifunctional polyamide comonomers, such as other diacid comonomers, diamine comonomers, aminoacid comonomers or lactam comonomers, or even by using a non-reactive additive capable of hydrogen bonding with the nylon 66 polymer, such as 7-naphthotriazinyl-3-phenylcoumarin, for example.
According to one aspect of the present invention, therefore, there is provided a process for preparing a textured nylon 66 multifilament yarn having a relative viscosity of about 50 to about 80, involving draw-texturing a feed yarn of denier about 15 to about 250 and of elongation (E.sub.b) about 70 to about 100% at a temperature of about 200.degree. to about 240.degree. C., to provide a textured yarn of elongation of less than about 35%, preferably less than 30%, characterized in that the texturing speed is at least about 900 mpm, preferably at least about 1000 mpm, and the feed yarn is a polymer of nylon 66 containing a minor amount of such bifunctional polyamide comonomer or of a non-reactive additive capable of hydrogen bonding with the nylon 66 polymer, and preferably as indicated herein.
According to another aspect of the present invention, there is provided a partially-oriented nylon 66 polymer multifilament yarn of denier about 15 to about 250 and of elongation (E.sub.b) about 70 to about 100%, preferably about 75 to about 95%, the polymer being of relative viscosity about 50 to about 80, characterized in that the polymer contains a minor amount, preferably, by weight, about 2 to about 8%, of a bifunctional polyamide comonomer or a non-reactive additive capable of hydrogen bonding with the nylon 66 polymer, and that the yarn has a draw-tension (DT) in g/d of between about 0.8 and about 1.2, preferably between about (140/E.sub.b -0.8) and about 1.2. Preferred such yarns are characterized by a draw modulus (M.sub.D) of about 3.5 to about 6.5 g/d and by a draw stress (.sigma..sub.D) of about 1.0 to about 1.9 g/d, measured at 75.degree. C. and a draw ratio of 1.35X, with apparent draw energy (E.sub.D).sub.a of about 0.2 to about 0.5. Preferred such yarns are also characterized by a TMA maximum dynamic extension rate (.DELTA.L/.DELTA.T.sub.1).sub.max between about 100.degree.-150.degree. C. under 300 mg/pre-tension, of about 0.05 to about 0.15%/.degree.C., and a sensitivity of (.DELTA.L/.DELTA.T.sub.1).sub.max to stress (.sigma.), d(.DELTA.L/.DELTA.T.sub.1).sub.max /d.sigma., as measured at 300 mg/d of about 3.times.10.sup.-4 to 7.times.10.sup.-4 (%/.degree.C.)/(mg/d).
In preferred partially-oriented nylon 66 polymer multifilament yarn in accordance with the invention employing N6,66 polymer, an RV of 60-70 is especially preferred. When Me5-6,66 polymer is employed, an RV of 50-60 is preferred.
According to another aspect of the present invention, there is provided a process for preparing a multifilament spin-oriented yarn of nylon 66 polymer of denier about 15 to about 250, by melt-spinning nylon 66 polymer of relative viscosity at least about 50 to about 80 at a spinning withdrawal speed of at least about 4500 meters/minute, preferably more than 5000 mpm, and preferably not more than about 6500 mpm characterized in that the nylon 66 polymer contains a minor amount of such bifunctional polyamide comonomer or of non-reactive additive capable of hydrogen bonding with the nylon 66 polymer. Preferred spinning conditions are a polymer extrusion temperature (T.sub.p) 20.degree. to 60.degree. C. above the polymer melting point (T.sub.m), preferably to 20.degree. to 40.degree. C. above T.sub.m. A spinneret capillary of dimensions such that the diameter (D) is about 0.15 to about 0.30 mm, preferably is about 0.15 to about 0.23 mm, and the length/diameter (L/D) ratio is at least about 1.75, preferably is at least about 2, especially is at least about 3, such that the value of the expression, L/D.sup.4, is at least about 100 mm.sup.-3, preferably at least about 150 mm.sup.-3, especially at least about 200 mm.sup.-3, providing an extent of melt attenuation, as given by the ratio, D.sup.2 /dpf, between about 0.010 to 0.045, quenching of the freshly-melt-spun filaments with a flow of air of more than about 50% RH, especially at least about 70% RH, at a temperature of about 10.degree. C. to about 30.degree. C. and at a velocity of about 10 to about 50 mpm, preferably of about 10 to 30 mpm, and convergence of the filaments between about 75 to 150 cm, preferably between about 75 to 125 cm, from the face of the spinneret.
According to a further aspect of the invention, there is provided a textured nylon 66 multifilament yarn having an elongation (E.sub.b) less than about 35%, preferably less than about 30%, and a relative viscosity of about 50 to about 80, characterized by the yarn consisting essentially of nylon 66 polymer containing a minor amount, preferably by weight about 2 to about 8%, of such bifunctional polyamide comonomer or of non-reactive additive capable of hydrogen bonding with the nylon 66 polymer.
In preferred textured nylon 66 polymer multifilament yarn in accordance with the invention employing N6,66 polymer, an RV of 60-70 is especially preferred. When Me5-6,66 polymer is employed, an RV of 50-60 is preferred.
Further aspects of the invention will appear, e.g., further processes for using the new yarns and products produced.